Nonwoven fabric and tea bag

ABSTRACT

A nonwoven fabric characterized in that the nonwoven fabric is a thermoplastic synthetic fiber nonwoven fabric having a fabric weight of 7 to 50 g/m 2 , an average yarn diameter of 7 to 40 μm, a partial heat contact bonding ratio of 5 to 30% and a content of a delustering agent of 0.5% by weight or less, or a nonwoven fabric laminate the major component of which is the thermoplastic synthetic fiber nonwoven fabric, and that the nonwoven fabric has a maximum opening diameter of 200 to 2,000 μm, and shows a transparency of 50% or more, a powder leakage ratio of 10% by weight or less and a hydrophilicity of less than 10 sec, and a tea bag in which the nonwoven fabric is used.

FIELD OF THE INVENTION

The present invention relates to a nonwoven fabric and a tea bag inwhich the nonwoven fabric is used.

BACKGROUND ART

When components of tea, such as black tea, green tea and oolong tea, areto be extracted, the tea bag system has often been used in a simplemethod. Generally, paper is often used as a tea bag material for a teabag. However, because the paper has a dense structure, the paper used asa tea bag material includes the following problems: although the powderleakage is decreased, the paper shows poor transparency and tea leavesin a tea bag are hardly seen; and the paper cannot be heat sealed.

Furthermore, a nonwoven fabric of thermoplastic synthetic fiber hasrecently been used as a tea bag material. The nonwoven fabric isprepared by compositing a filaments yarn nonwoven fabric and anextremely thin yarn nonwoven fabric, and the powder leakage is decreasedby utilizing a filtering effect of the extremely thin yarn. Such aconventional nonwoven fabric of thermoplastic synthetic fiber isexcellent in that it can be heat sealed, and that the powder leakage isdecreased. However, the nonwoven fabric has the problem that tea leavesin a tea bag cannot be seen due to insufficient transparency, and thelike problem. In particular, when tea leaves of a high grade are used,that the state of tea leaves in a tea bag cannot be seen is a greatdisadvantage.

In order to improve the transparency of a tea bag and the high-gradefeeling it gives, a coarse plain gauze fabric is processed to form a bagshape. However, the resultant tea bag allows much powder leakage.Moreover, the tea bag has a problem regarding in waste treatment.

Japanese Unexamined Patent Publication (Kokai) No. 2001-131826 describesbiodegradable monofilaments for tea bags composed of a poly(L-lacticacid), having a size of 15 to 35 dtex, and showing a boil-off shrinkageof 20% or less. However, the invention relates to a tea bag preparedfrom a plain gauze fabric in which monofilaments are used. The tea bagtherefore has the problem that it allows much powder leakage when thetransparency of the fabric is increased.

Japanese Unexamined Patent Publication (Kokai) No. 2002-105829 describesa method of making a nonwoven fabric, of a thermoplastic aliphaticpolyester filament yarn, flexible by subjecting the fabric to bendingtreatment. The patent publication discloses a filament yarn nonwovenfabric having a fabric weight of 15 to 200 g/m², a size of 1.0 to 12dtex and 4 to 50% of a partial heat contact bonded portion. Moreover,the fabric has no problem about refuse in waste treatment because thefabric is biodegradable. However, there is no description in the patentpublication of a nonwoven fabric or a tea bag excellent in transparency,powder leakage, and the like.

Japanese Unexamined Patent Publication (Kokai) No. 9-142485 describes ashort fiber nonwoven fabric in which cellulose fiber and biodegradablealiphatic polyester fiber are mixed. The nonwoven fabric contains shortfiber that has a size of 1 to 10 denier, is partially heat bonded with aratio of 5 to 50% or entirely heat bonded, has excellent strength andprocessability, and is easily degraded by microorganisms. The nonwovenfabric is utilized for a bag for raw refuse, etc. However, there is nodescription in the patent publication of a nonwoven fabric or a tea bagexcellent in transparency, powder leakage, and the like.

Japanese Unexamined Patent Publication (Kokai) No. 7-189136 discloses alight-shielding nonwoven fabric for which a sheath-core yarn is used. Asheath-core conjugate yarn formed out of a polymer as a sheath componentthat contains a decreased amount of inorganic particles, and a polymeras a core component that contains an increased amount of inorganicparticles is used for the nonwoven fabric. Because the nonwoven fabriccontains a relatively large amount of inorganic particles in the corecomponent, the nonwoven fabric has excellent shielding properties, andis useful for a printing substrate. However, there is no description inthe patent publication of a nonwoven fabric or a tea bag excellent intransparency, powder leakage, and the like.

Although Patent Publication WO 02/48443 discloses a nonwoven fabricmaterial for tea bags that is improved in transparency, there is nodescription about powder leakage.

DISCLOSURE OF THE INVENTION

An object of the present invention is to solve the above problems, andto provide a nonwoven fabric excellent in transparency, showingdecreased powder leakage and excellent bag formability, and causing norefuse problem in waste treatment, and to provide tea bags composed ofthe nonwoven fabric.

The present inventors have discovered that a nonwoven fabric excellentin transparency and showing decreased powder leakage can be obtained bycombining a thermoplastic synthetic fiber material, a content of adelustering agent, a yarn diameter of a yarn forming the nonwovenfabric, a fabric weight, heat contact bonding conditions, and the like,and by further investigating the transparency and the maximum openingdiameter of the fiber material. The present invention has thus beenachieved.

That is, the present invention is as explained below.

1. A nonwoven fabric characterized in that the nonwoven fabric is athermoplastic synthetic fiber nonwoven fabric having a fabric weight of7 to 50 g/m², an average yarn diameter of 7 to 40 μm, a partial heatcontact bonding ratio of 5 to 30% and a content of a delustering agentof 0.5% by weight or less, or a nonwoven fabric laminate the majorcomponent of which is the thermoplastic synthetic fiber nonwoven fabric,and that the nonwoven fabric has a maximum opening diameter of 200 to2,000 μm, and shows a transparency of 50% or more, a powder leakageratio of 10% by weight or less and a hydrophilicity of less than 10 sec.

2. The nonwoven fabric according to 1 mentioned above, wherein thenonwoven fabric is characterized in that the nonwoven fabric is athermoplastic synthetic fiber nonwoven fabric having a fabric weight of12 to 30 g/m², an average yarn diameter of 12 to 30 μm, a partial heatcontact bonding ratio of 5 to 30% and a content of a delustering agentof 0.2% by weight or less, or a nonwoven fabric laminate the majorcomponent of which is the thermoplastic synthetic fiber nonwoven fabric,and that the nonwoven fabric has a maximum opening diameter of 400 to1,650 μm, and shows a transparency of 60% or more, a powder leakageratio of 5% by weight or less and a hydrophilicity of less than 10 sec.

3. The nonwoven fabric according to 1 mentioned above, wherein thenonwoven fabric is a laminate of a thermoplastic synthetic fibernonwoven fabric having an average yarn diameter of 7 to 15 μm and athermoplastic synthetic fiber nonwoven fabric having an average yarndiameter of 15 to 40 μm.

4. The nonwoven fabric according to any one of 1 to 3 mentioned above,wherein the thermoplastic synthetic fiber nonwoven fabric is aspun-bonded nonwoven fabric composed of a polyolefin filament yarn.

5. The nonwoven fabric according to any one of 1 to 3 mentioned above,wherein the thermoplastic synthetic fiber nonwoven fabric is aspun-bonded nonwoven fabric composed of a polyester filament yarn.

6. The nonwoven fabric according to 5 mentioned above, wherein thethermoplastic synthetic fiber nonwoven fabric is a spun-bonded nonwovenfabric composed of an aliphatic polyester filament yarn.

7. The nonwoven fabric according to 6 mentioned above, wherein thealiphatic polyester filament yarn is a filament yarn of a polyesterselected from a poly(D-lactic acid), a poly(L-lactic acid), a copolymerof D-lactic acid and L-lactic acid, a copolymer of D-lactic acid and ahydroxycarboxylic acid, a copolymer of L-lactic acid and ahydroxycarboxylic acid, a copolymer of D-lactic acid, L-lactic acid anda hydroxycarboxylic acid, or a blend of these polymers.

8. The nonwoven fabric according to any one of 1 to 7 mentioned above,wherein a synthetic resin or a fibrous material of 2 to 15 g/m² having amelting point lower than that of the thermoplastic synthetic fiber by 30to 200° C. is laminated to the thermoplastic synthetic fiber nonwovenfabric.

9. A tea bag prepared by filling a tea material to be extracted, into abag composed of the nonwoven fabric according to any one of 1 to 8mentioned above, and sealing the tea material.

10. The tea bag according to 9 mentioned above, wherein the bag istetrahedral-shaped.

11. The tea bag according to 9 or 10 mentioned above, wherein the teamaterial to be extracted is black tea, green tea or oolong tea.

The present invention is explained below in detail.

Examples of the thermoplastic synthetic fiber forming the nonwovenfabric in the present invention include polyolefin fiber such aspolyethylene fiber, polypropylene fiber and copolymerized polypropylenefiber, polyester fiber such as poly(ethylene terephthalate) fiber,copolymerized polyester fiber and aliphatic polyester fiber, compositeyarn of core-sheath structure composed of a sheath that is formed out ofpolyethylene, polypropylene, copolymerized polyester, aliphaticpolyester, or the like, and a core that is formed out of polypropylene,poly(ethylene terephthalate), or the like, and biodegradable fiber ofpoly(lactic acid), poly(butylene succinate), poly(ethylene succinate),or the like. Short fiber or filament yarn is used for the above fibers.

These fibers may be used singly, or at least two of them may be used asa laminate. For example, a laminated nonwoven fabric obtained bystacking a filament yarn nonwoven fabric and short fiber, and heatembossing the stacked materials may be used.

In the present invention, the nonwoven fabric of thermoplastic syntheticfiber has a fabric weight of 7 to 50 g/m², preferably 10 to 40 g/m², andmore preferably 12 to 30 g/m². When the fabric weight is in the aboverange, the nonwoven fabric shows good transparency, has suitable gapsamong yarns, and exhibits decreased powder leakage.

In the present invention, the nonwoven fabric of thermoplastic syntheticfiber has an average yarn diameter of 7 to 40 μm, preferably 10 to 35μm, and more preferably 12 to 30 μm. When the average yarn diameter isin the above range, the nonwoven fabric shows good transparency anddecreased powder leakage.

In the present invention, the partial heat contact bonding ratio of thenonwoven fabric of thermoplastic synthetic fiber is from 5 to 30%, andpreferably from 7 to 27%. Partial heat contact bonding of the nonwovenfabric decreases gaps among yarns forming the nonwoven fabric, and canadjust the transparency, powder leakage, strength, stiffness, and thelike of the nonwoven fabric. When the partial heat contact bonding ratiois less than 5%, bonded portions formed by contact bonding aredecreased, and powder leakage increases. On the other hand, when thepartial heat contact bonding ratio exceeds 30%, the powder leakage isdecreased, and the transparency is improved because bonded portions areincreased; however, the feel of the fabric is likely to become stiff,and the liquid permeability tends to lower. In addition, the partialheat contact bonding ratio represents a ratio of an area of heat contactbonded portions to the entire area of the nonwoven fabric.

Examples of the method of partial heat contact bonding include a methodcomprising passing a nonwoven fabric through a pair of heating rollsconsisting of an emboss roll having an uneven surface structure and aflat roll having a smooth surface, thereby forming heat contact bondedportions uniformly dispersed over the entire nonwoven fabric.

Because a higher transparency (poor shielding properties) of thenonwoven fabric of the invention is preferred, a decreased amount of aninorganic additive, that is a delustering agent in the yarn forming thenonwoven fabric of thermoplastic synthetic fiber, is preferred.Accordingly, a nonwoven fabric of a bright yarn or an ultra-bright yarnis preferred. The content of the delustering agent is preferably 0.5% byweight or less, and more preferably 0.2% by weight or less. Althoughexamples of the delustering agent include conventionally used metaloxides such as titanium oxide, magnesium stearate and calcium stearate,titanium oxide is preferred in view of the particle stability andspinning stability.

For the nonwoven fabric of the invention, a combination of a thin yarnlayer and a thick yarn layer further improves the powder leakage andtransparency. For example, a laminate of a nonwoven fabric ofthermoplastic synthetic fiber having an average yarn diameter as thin as7 to 15 μm and a fabric weight of 3 to 20 g/m² and a nonwoven fabric ofthermoplastic synthetic fiber having an average yarn diameter as thickas 15 to 40 μm and a fabric weight of 4 to 30 g/m² is preferred.

Because the nonwoven fabric of the present invention is used in abag-shaped article such as a tea bag, it is preferred that the nonwovenfabric show a high bonding strength when heat sealed by a bag-makingmachine. In order for the nonwoven fabric of thermoplastic syntheticfiber to show good bonding strength and good heat sealability, asynthetic resin or a fibrous material of the resin having a meltingpoint lower than that of the nonwoven fabric by preferably 30 to 200°C., more preferably 50 to 160° C. is preferably laminated to thenonwoven fabric of thermoplastic synthetic fiber on at least one side inan amount of 2 to 15 g/m², and more preferably 4 to 12 g/m².

As a result of laminating a synthetic resin or a fibrous materialthereof having a melting point lower than that of a nonwoven fabric ofthermoplastic synthetic fiber to the nonwoven fabric, whereby thelaminate is made to have a difference in melting point between the twomaterials, the synthetic resin or fibrous material alone having a lowmelting point is softened or melted during heat sealing, and acts as anadhesive to effectively give a high heat sealing strength.

When the lamination amount of the synthetic resin or fibrous materialhaving a low melting point is in the above range, an amount of amaterial that contributes as an adhesive is suitable, and an adequateheat seal strength is obtained. Moreover, the transparency of thenonwoven fabric is high, and the production cost is low. In addition,the heat seal strength is preferably 1 N/5 cm or more, and morepreferably 3 N/5 cm or more.

Examples of the synthetic resin or fibrous material thereof having a lowmelting point include a polyolefin resin such as a linear low densitypolyethylene, a low density polyethylene, a polypropylene and acopolymerized polypropylene, a polyester resin such as a linearpolyester and a copolymerized polyester, a synthetic resin such as anethylene-vinyl acetate copolymer resin, a polyamide resin and asynthetic rubber resin or a fibrous material of the synthetic resin, acomposite fiber having a core-sheath structure that is composed of acombination of a low melting point sheath component such as apolyethylene, a polypropylene or a copolymerized polyester, and a highmelting point core component such as a polypropylene, a copolymerizedpolyester, nylon-6 or a poly(ethylene terephthalate), and a low-meltingpoint fiber such as aliphatic acid ester fiber, for example, poly(lacticacid) fiber and poly(butyl succinate) fiber.

Examples of the method of laminating the synthetic resin or a fibrousmaterial thereof having a low melting point to the nonwoven fabric ofthermoplastic synthetic fiber include a curtain spraying methodcomprising melting the resin, and coating the nonwoven fabric with theresultant semi-molten resin or fibrous material thereof, a coatingmethod comprising injecting the resin in a molten state through a nozzleso that the nonwoven fabric is coated with the resin, and a methodcomprising forming a fiber web out of mixed fiber of a high meltingpoint fiber and a low melting point fiber, or a short fiber of compositefiber by carding procedure or an air-lay procedure, stacking the fiberweb and the nonwoven fabric of thermoplastic synthetic fiber, andbonding the stacked materials with a heat roll, or the like, to give alaminate of a nonwoven fabric.

Furthermore, in the present invention, it is preferred that the nonwovenfabric of thermoplastic synthetic fiber causes no problem in wastetreatment, and that the nonwoven fabric be the one of aliphaticpolyester filament yarn composed of a biodegradable resin.

For example, a poly(lactic acid) polymer is preferably used as thebiodegradable resin. Preferred examples of the poly(lactic acid) polymerinclude a poly(D-lactic acid), a poly(L-lactic acid), a copolymer ofD-lactic acid and L-lactic acid, a copolymer of D-lactic acid and ahydroxycarboxylic acid, a copolymer of L-lactic acid and ahydroxycarboxylic acid, a copolymer of D-lactic acid and L-lactic acidand a hydroxycarboxylic acid, or a blend of these polymers. The meltingpoints of the above polymers are preferably 100° C. or more.

Examples of the hydroxycarboxylic acid used for the above poly(lacticacid) polymer include glycolic acid, hydroxybutyric acid, hydroxyvalericacid, hydroxypentanoic acid, hydroxycaproic acid, hydroxyheptanoic acidand hydroxyoctanoic acid. Of these acids, glycolic acid andhydroxycaproic acid are preferred.

Although there is no specific limitation on the molecular weight of thepoly(lactic acid) polymer, the weight average molecular weight is from10,000 to 1,000,000, and preferably from 30,000 to 500,000 in view ofthe spinnability and the filament strength.

In order to increase the heat resistance, mechanical strength,polymerization degree, flexibility, and the like, additives such as anucleating agent are added to the above polymer. Examples of thenucleating agent include talc, titanium oxide, calcium carbonate,magnesium carbonate and carbon. In order to make the crystallinity ofpoly(lactic acid) fiber fall in a range of 10 to 40%, an addition amountof the nucleating agent is preferably 0.5% by weight or less, and morepreferably 0.2% by weight or less. When the crystallinity of the polymeris in the above range, the heat resistance and mechanical strength ofthe polymer is sufficient, and the heat contact bondability andbiodegradability of the polymer are good.

There is no specific restriction on the method of producing the nonwovenfabric. Known methods such as spin bonding, needle punching, air layingand water needling can be applied thereto. For example, when the spinbonding method is used, the method comprises melting a synthetic resinwith a melt spinning apparatus, injection spinning the molten resinthrough a spinneret, drawing the spun yarn with an air sucker, or thelike, opening and collecting the spun yarn on a conveyor net, passingthe yarn between an emboss roll and a smoothing roll, and partial heatcontact bonding the resultant web with a heat emboss roll to give anonwoven fabric.

In the present invention, a spin-bonded nonwoven fabric composed of apolyolefin filaments yarn or a polyester filaments yarn is a preferrednonwoven fabric because the formation is uniform, and in particular auniform nonwoven fabric can be obtained with low fabric weight. Theuniform nonwoven fabric with low fabric weight has the followingadvantages: no uneven fabric weight appears; gaps among yarns becomeuniform; distribution of the pore diameter becomes uniform; and thedisadvantage that powder leakage caused by large pores disappears. Thespun-bonded nonwoven fabric is preferred because it has a large strengthwith low fabric weight. For example, the variation ratio of a fabricweight, 10 cm×10 cm, is 10% or less, more preferably 7% or less, andstill more preferably 5% or less. In addition, variation ratio of afabric weight (%)=[(standard deviation)/(average fabric weight)]×100

The nonwoven fabric of the present invention has a maximum openingdiameter of 200 to 2,000 μm, preferably 300 to 1,800 μm, and morepreferably 400 to 1,650 μm. When the maximum opening diameter is lessthan 200 μm, gaps among yarns forming the nonwoven fabric are decreased,and the powder leakage is reduced; however, the transparency becomesinsufficient. On the other hand, when the maximum opening diameterexceeds 2,000 μm, gaps among the yarns are increased, and thetransparency is improved; however, the powder leakage is increased.

FIG. 1 shows the relationship (line 1, left hand side scale) between amaximum opening diameter and a transparency in examples of theinvention, and the relationship (line 2, right hand side scale) betweena maximum opening diameter and a powder leakage ratio. The following areevident from FIG. 1: when the maximum opening diameter is 200 μm ormore, the transparency of the nonwoven fabric is markedly improved, andthe powder leakage is low; however, when the maximum opening diameterexceeds 2,000 μm, the powder leakage ratio tends to rapidly increase.That is, for a nonwoven fabric, improvement of the transparency andsuppression of the powder leakage conflict each other. However, thepresent inventors have made improvement of the transparency andsuppression of the powder leakage compatible by making the maximumopening diameter fall in a range of 200 to 2,000 μm.

The transparency of the nonwoven fabric of the invention is 50% or more,preferably 55% or more, and more preferably from 60 to 100%. When thetransparency is less than 50%, the contents are hardly seen through thetea bag material, and the state thereof is unclear. The transparency isobtained, as described later, by measuring an Lw value of a white boardand an Lb value of a black board with a Macbeth spectrometer, anddetermining the difference between the Lw value and the Lb value.

The powder leakage ratio of the nonwoven fabric of the invention is 10%by weight or less, preferably 7% by weight or less, and more preferably5% by weight or less. When the powder leakage ratio exceeds 10% byweight, the powder leakage increases. As a result, use of the nonwovenfabric as a tea filter results in leakage of much powder in an extractedsolution, and making the tea agreeable becomes difficult due to the highcontent of a solid powder component. In addition, the method ofmeasuring powder leakage ratio is as described later.

The nonwoven fabric of the present invention is preferably excellent inhydrophilicity so that it is rapidly submerged under water withoutfloating on the surface when it is placed in hot water. Thehydrophilicity of the nonwoven fabric of the invention is less than 10sec, preferably less than 7 sec, and more preferably less than 5 sec. Inorder to make the hydrophilicity fall in a range of less than 10 sec,the nonwoven fabric should be coated with, for example, a hydrophilicagent in an amount of 0.05 to 5.0% by weight, and preferably 0.1 to 3%by weight. In addition, when a coating amount of the hydrophilic agentis excessive, the hydrophilic agent is dissolved. As result, use of thenonwoven fabric for food applications such as a tea bag causes aproblem.

Examples of the hydrophilic agent include an aqueous solution, an ethylalcohol solution or an ethyl alcohol-water mixture solution of such asurfactant used for food as a sorbitan aliphatic acid ester, apolyglycerin aliphatic acid ester or a sucrose aliphatic acid ester.Known methods such as a gravure roll system, a kiss roll system, animmersion system or a spray system can be used as the coating method.

The average apparent density of the nonwoven fabric of the presentinvention is preferably from 0.05 to 0.25 g/cm³, and more preferablyfrom 0.08 to 0.22 g/cm³. The average apparent density is related to afeel, stiffness, transparency and powder leakage of the nonwoven fabric.When the average apparent density falls in the above range, the nonwovenfabric is excellent in strength, flexibility and transparency, and showsreduced powder leakage because gaps among the yarns are suitable.Moreover, the nonwoven fabric shows excellent bag formability during bagforming.

The nonwoven fabric of the present invention is useful as a nonwovenfabric for a tea filter, and is preferably used as tea bags prepared bysubjecting the fabric to bag-making processing to form flat ortetrahedral-shaped bags, and filling a material to be extracted into thebags. There is no specific restriction on the method of bag-makingprocessing. For example, heat sealing, melt sticking sealing, meltcutting sealing, ultrasonic sealing, high frequency sealing, or the likesealing can be employed. Furthermore, known bag-making machines can beused.

As a material to be extracted, for example, as tea leaves, black tea,green tea or oolong tea is common. However, the material to be extractedis not restricted to the above teas, and roasted tea, green tea of amiddle grade, barley tea, a herb, or the like, may also be utilized.

The tea bag of the present invention may be a flat bag. However, a teabag having a three-dimensional shape is preferred for the followingreasons: the tea bag has a space, and tea leaves can be well observedbefore immersion in hot water; moreover, when the tea bag is placed inwater, the state of the tea can be observed much better; because thevolume within the tea bag is large, swelling and spreading of the tealeaves are good, and the tea is quickly extracted. Preferred examples ofthe three-dimensional shape include a tetragonal shape such as atriangular cone shape or a TetraPak shape.

In general, tea bags having a three-dimensional shape are filled withmaterial to be extracted, packed in boxes, and marketed. The tea bagseach have a folded shape when packed in boxes. However, when consumerstake out the tea bags from the boxes and use them, each tea bagpreferably recovers the initial three-dimensional shape rapidly. Becausethe nonwoven fabric of the present invention has an average yarndiameter as thick as 7 to 40 μm, it has good resilient properties and asuitable stiffness. As a result the nonwoven fabric is excellent in athree-dimensional shape recovery.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing the relationship (line 1: left hand sidescale) between a maximum opening diameter and a transparency of anonwoven fabric in examples of the present invention, and therelationship (line 2: right hand side scale) between a maximum openingdiameter and a powder leakage ratio thereof.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is further explained below by making reference toexamples. However, the present invention is in no way restrictedthereto.

In addition, measurement methods, evaluation methods, and the like, areas explained below.

(1) Fabric Weight (g/m²)

Measurements are made in accordance with JIS L 1906. Samples, each 20 cm(longitudinal)×25 cm (lateral), are cut out at three sites,respectively. The weight of each sample is determined, and the fabricweight in terms of weight per unit area is obtained from the average.

(2) Average Yarn Diameter (μm)

Microscopic photographs of yarns are taken at magnifications of ×500.The average yarn diameter is obtained from an average of 10 yarns.

(3) Transparency (%)

The reflectivity of a sample is measured with a Macbeth spectrometer ofCE-3000 type (manufactured by Sakata Ink Co., Ltd.). A differencebetween a white board Lw0 value and a black board Lb0 value is used as astandard. From an Lw value and an Lb value of a sample, the transparencyof the sample is determined from the following formula:transparency (%)=[ΔL/ΔL0]×100wherein ΔL0=Lw0−Lb0, and ΔL=Lw−Lb.

(4) Powder Leakage Ratio (wt. %)

About 2 g of a filtering material for spinning (metal powder CR 53,particle size classification of 25/50 mesh, 650/300 μm, manufactured byTaiheiyo Metal) is weighed out, and the weight W1 (g) is measured. Thefiltering material is placed on a nonwoven fabric, 25 cm×25 cm, andshaken at 60 rpm for about 5 minutes with a shaking machine. The weightW2 (g) of a filtering material that has passed through the nonwovenfabric is then measured, and the powder leakage ratio is obtained fromthe following formula:powder leakage ratio (wt. %)=[W 2/W 1]×100

(5) Air Permeability

The air permeability is obtained in accordance with JIS L-1906 (Frajuremethod).

(6) Hydrophilicity

The hydrophilicity is measured in accordance with JIS L-1906 (droppingmethod). Water is dropped on a sample, and a time necessary for thesample to permeate is measured. The results are evaluated according tothe following criteria:

{circle around (⊙)}: Water permeates the sample within 5 sec.

O: Water permeates the sample within 10 sec.

X: Water does not permeate the sample for 10 sec or more.

(7) Average Apparent Density

The apparent density of a sample in terms of a weight per unit volume isobtained from a fabric weight and a thickness of the sample under a loadof 10 kPa. The average apparent density of the sample is obtained froman average of the measured values at three sites.

(8) Maximum Opening Diameter

The maximum opening diameter is obtained in accordance with JIS K-3832(bubble point method).

A circular sample 40 mm in diameter is immersed in a liquid so that allthe pores of the sample are filled with the liquid by capillary action.Air pressure is gradually applied to the sample from the back sidethereof. When the air pressure overcomes a liquid surface tension withina capillary tube, an air bubble comes out; the air pressure is measured.The initial bubble comes out of an opening having the maximum openingdiameter. The maximum opening diameter can be calculated by determiningthe air pressure when the initial bubble comes out.

(9) Seal Strength

Six samples, each being 5 cm wide and 30 cm long, are cut out from anonwoven fabric in the longitudinal direction. Six samples are preparedin the same manner except that they are cut out in the lateraldirection. Each sample is sealed by ultrasonic waves at three sites witha 1-mm thick round blade-shaped head horn of an ultrasonic wave sealingmachine having an output at 40 kHz (manufactured by Brother Industries,Ltd.). Each sealed sample is attached to a tensile testing machine inthe vertical direction of the machine. The sample is pulled at a tensilerate of 10 cm/min with a chuck-to-chuck distance of 10 cm, and a maximumstrength is measured. The average of the six samples is determined, anddefined as a seal strength.

(10) Melt Flow Rate (MFR)

Measurements on a sample are made in accordance with JIS K-7210 “Flowtest method of thermoplastic resin” (condition 14 in Table 1: a testtemperature of 230° C. and a test load of 21.18 N), and the MFR isdetermined.

(11) Intrinsic Viscosity ([η])

The intrinsic viscosity ([η]) is a value obtained from the followingdefinition formula:[η]=lim (η_(r)−1)/CC→0wherein η_(r) (that is defined as a relative viscosity) is a valueobtained by dividing a viscosity of a diluted solution at 35° C. of apolymer dissolved in an o-chlorophenol solvent having a purity of 98% ormore by the viscosity of the above solvent determined at the sametemperature, and C is a polymer concentration in terms of g/100 ml ofthe above solution.

EXAMPLES 1 TO 5, COMPARATIVE EXAMPLES 1 TO 3

A known spun bond method was used. A polypropylene resin showing a MFRof 39, and having a titanium oxide content of 0.1% by weight was spunthrough a spinneret by a melt spinning system. The spun yarn was drawnwith a high speed drawing apparatus, opened, and collected to give afiber web. The procedure was repeated while a fabric weight and a yarndiameter were varied to give various webs. Each web was then heatcontact bonded by heat pressing between an emboss roll and a smooth rollto give a spun-bonded, partial heat contact bonded nonwoven fabric ofpolypropylene filaments yarn.

In any of Examples 1 to 5, each nonwoven fabric was then coated with asorbitan aliphatic acid ester as a hydrophilic agent by a gravure rollsystem in an amount of 0.2 to 2.0% by weight, and dried at 130° C. togive a coated nonwoven fabric. In addition, the nonwoven fabrics werenot coated with the hydrophilic agent in Comparative Examples 1 to 3.

Furthermore, in each of Examples 4 and 5, two types of thermoplasticsynthetic fiber webs differing from each other in a yarn diameter and afabric weight were used as an upper layer and a lower layer,respectively, to give laminate of nonwoven fabrics.

Table 1 shows properties of the nonwoven fabrics thus obtained. Inaddition, the numerical values in parentheses in the column of “airpermeability” are values each obtained from a sample prepared bystacking two initial samples.

TABLE 1 Example Comp. Example 1 2 3 4 5 1 2 3 Upper Fabric weight (g/m²) 12 25 40 15 10  10 65 40 layer Average yarn diameter (μm)  20 25 27 3018  44 15 27 Lower Fabric weight (g/m²) — — — 10 15 — — — layer Averageyarn diameter (μm) — — — 25 25 — — — Fabric weight (g/m²)  12 25 40 2525  10 60 40 Partial heat contact bonding  25 15 10 15 15   5 35 10ratio (%) Coating amount of hydrophilic   0.2 0.4 2.0 0.2 0.3   0 0 0agent(wt. %) Average apparent density (g/cm³)   0.11 0.15 0.22 0.14 0.15  0.04 0.35 0.22 Air permeability (ml/cm²/sec)  (180) 250 210 295 280 (235) 75 210 Transparency(%)  75 71 60 77 70  80 30 34 Powder leakageratio (wt. %)   4.5 1.5 0.7 2.5 1.0  19.5 0.2 0.7 Hydrophilicity(sec) ⊚⊚ ⊚ ⊚ ⊚ X X X Maximum opening diameter (μm) 1650 650 350 750 650 2800125 345 Seal Longitudinal   6.0 13.5 18.5 12.0 13.0   0.6 26.0 18.0strength Lateral   4.0 7.5 12.5 8.5 7.2   0.3 17.5 12.0 (N/5 cm) Contentof delustering agent (wt %)   0.1 0.1 0.1 0.1 0.1   0.1 0.1 0.7

It can be understood from Table 1 that the nonwoven fabrics of thepresent invention (Examples 1 to 5) were excellent in transparency andhydrophilicity and showed decreased powder leakage. Moreover, as aresult of measuring a variation ratio of a fabric weight, the ratio was6.5% in Example 2, and 4.7% in Example 5.

In contrast to the above results, the nonwoven fabric in ComparativeExample 1 showed much powder leakage and poor hydrophilicity because thefabric had no hydrophilic agent coating, although the fabric showed goodtransparency. Moreover, the nonwoven fabric in Comparative Example 2 hadlarge fabric weight, and a high density of the yarn forming the fabric,and as a result, the fabric showed decreased powder leakage; however,the fabric showed considerably lowered transparency, and poorhydrophilicity because the fabric had no hydrophilic agent coating. Thenonwoven fabric in Comparative Example 3 had a large content of adelustering agent, and as result the fabric showed lowered transparency.

EXAMPLES 6 TO 10, COMPARATIVE EXAMPLES 4 TO 5

A partially heat contact bonded, spin-bonded nonwoven fabric of apolyester filaments yarn was obtained in the same manner as in Example 1except that a bright resin of a poly(ethylene terephthalate) (intrinsicviscosity of 0.76, titanium oxide content of 0.05% by weight) was usedin place of the polypropylene resin.

The nonwoven fabrics were then coated with a sorbitan aliphatic acidester as a hydrophilic agent in an amount of 0.1 to 0.5% by weight witha gravure roll, and dried at 130° C. In addition, the nonwoven fabricsin Comparative Examples 4 and 5 were not coated with a hydrophilicagent.

Furthermore, in each of Examples 9 and 10, two types of thermoplasticsynthetic fiber webs differing from each other in a yarn diameter and afabric weight were used as an upper layer and a lower layer,respectively, to give a laminate of nonwoven fabrics.

Table 2 shows properties of the nonwoven fabrics thus obtained. Inaddition, the numerical values in parentheses in the column of “airpermeability” are values each obtained from a sample prepared bystacking two initial samples.

TABLE 2 Example Comp. Example 6 7 8 9 10 4 5 Upper Fabric weight (g/m²) 12 20 40   8 10  10 65 layer Average yarn diameter (μm)  19 22 24  1414  45 13 Lower Fabric weight (g/m²) — — —   8 15 — — layer Average yarndiameter (μm) — — —  18 25 — — Fabric weight (g/m²)  12 20 40  16 25  1065 Partial heat contact bonding ratio (%)  25 15 10  25 15   3 40Coating amount of hydrophilic   0.1 0.2 0.5   0.3 0.3   0 0 Agent (wt.%) Average apparent density (g/cm³)   0.11 0.15 0.20   0.14 0.18   0.030.37 Air permeability (ml/cm²/sec)  (170) 230 185  (145) 220  (265) 60Transparency (%)  72 67 57  71 65  81 33 Powder leakage ratio (wt. %)  4.8 1.3 0.5   1.8 0.7  19.6 0.2 Hydrophilicity (sec) ⊚ ⊚ ⊚ ⊚ ⊚ X XMaximum opening diameter (μm) 1620 630 430 1150 570 2700 110 SealLongitudinal   4.0 10.5 15.5   6.5 12.5   0.3 21.0 strength Lateral  3.0 6.5 11.0   3.7 7.8   0.1 13.5 (N/5 cm) Content of delusteringagent (wt %)   0.05 0.05 0.05   0.05 0.05   0.05 0.05

It can be understood from Table 2 that the nonwoven fabrics of thepresent invention (Examples 6 to 10) were excellent in transparency andhydrophilicity and showed decreased powder leakage.

In contrast to the above results, the nonwoven fabric in ComparativeExample 4 showed much powder leakage and poor hydrophilicity, althoughthe fabric showed good transparency. Moreover, because the yarn formingthe nonwoven fabric in Comparative Example 5 had a large yarn density,the fabric showed decreased powder leakage; however, the fabric showedpoor transparency and hydrophilicity.

EXAMPLES 11 TO 15, COMPARATIVE EXAMPLES 6 TO 7

A partially heat contact bonded nonwoven fabric of an aliphaticpolyester filaments yarn was obtained in the same manner as in Example 1except that a biodegradable resin (titanium oxide content of 0.03% byweight) of a poly(lactic acid)(copolymerization ratio (molecular ratio)of D form/L form of 1.5/98.5; melting point of 173° C.; MFR of 13 g/10min) was used in place of the polypropylene resin.

The nonwoven fabrics were then coated with a sorbitan aliphatic acidester as a hydrophilic agent in an amount of 0.2% by weight with agravure roll, and dried at 130° C. In addition, the fabrics inComparative Examples 6 and 7 were not coated with a hydrophilic agent.

Furthermore, in each of Examples 14 and 15, two types of thermoplasticsynthetic fiber webs differing from each other in a yarn diameter and afabric weight were used as an upper layer and a lower layer,respectively, to give a laminate of nonwoven fabrics.

Table 3 shows properties of the nonwoven fabrics thus obtained. Inaddition, the numerical values in parentheses in the column of “airpermeability” are values each obtained from a sample prepared bystacking two initial samples.

TABLE 3 Example Comp. Example 11 12 13 14 15 6 7 Upper Fabric weight(g/m²)  12 20 30   8 10  11 64 layer Average yarn diameter (μm)  14 1820   12 14  44 13 Lower Fabric weight (g/m²) — — —   8 15 — — layerAverage yarn diameter (μm) — — —   15 20 — — Fabric weight (g/m²)  12 2030   16 25  11 64 Partially heat contact bonding ratio (%)  25 15 5   2515   4 38 Coating amount of hydrophilic   0.1 0.2 0.5   0.1 0.2   0 0agent (wt. %) Average apparent density (g/cm³)   0.13 0.17 0.20   0.150.21   0.03 0.36 Air permeability (ml/cm²/sec)  (170) 215 190 (140) 205 (260) 58 Transparency (%)  76 70 64   73 68  80 29 Powder leakage ratio(wt. %)   3.3 1.1 0.7   1.9 0.8  19.4 0.3 Hydrophilicity (sec) ⊚ ⊚ ⊚ ⊚ ⊚X X Maximum opening diameter (μm) 1650 830 670  960 740 2560 120 SealLongitudinal   3.7 9.5 13.5   5.8 10.7   0.3 20.5 strength Lateral   2.86.3 10.2   4.1 7.4   0.1 13.0 (N/5 cm) Content of delustering agent (wt%)   0.03 0.03 0.03   0.03 0.03   0.03 0.03

It can be understood from Table 3 that the nonwoven fabrics of thepresent invention (Examples 11 to 15) were excellent in transparency andhydrophilicity, showed decreased powder leakage, and were also excellentin biodegradability.

In contrast to the above results, the nonwoven fabric in ComparativeExample 6 showed much powder leakage and poor hydrophilicity, althoughthe fabric showed good transparency. Moreover, because the yarn formingthe nonwoven fabric in Comparative Example 7 had a large yarn density,the fabric showed decreased powder leakage; however, the fabric showedpoor transparency and hydrophilicity.

EXAMPLE 16

The spun-bonded nonwoven fabric of a polypropylene filaments yarnobtained in Example 2 was coated on one side with a fibrous material inan amount of 10 g/m² by curtain spraying a hot melt resin to give alaminated nonwoven fabric. In addition, a polypropylene resin (tradename of YH 151-1P, manufactured by Hitachi Chemical Polymer Co., Ltd.,melting point of 145° C.) was used as the hot melt resin. The meltingpoint difference between the filaments yarn and the hot melt resin was60° C. The laminated nonwoven fabric thus obtained was then coated witha hydrophilic agent in the same manner as in Example 2 to give anonwoven fabric.

The nonwoven fabric thus obtained had the following properties: a fabricweight of 35 g/m²; a variation ratio in the fabric weight of 3.8%; apartial heat contact bonding ratio of 15%; a coating amount of ahydrophilic agent of 0.4% by weight; an average apparent density of 0.22g/cm³; a transparency of 69%; a powder leakage ratio of 1.2% by weight;a maximum opening diameter of 630 μm; and good hydrophilicity ({circlearound (⊙)}). Moreover, the strength of a seal formed by a heat sealingmachine at 130° C. was 8.5 N/5 cm (longitudinal) and 4.3 N/5 cm(lateral). The nonwoven fabric was excellent in heat sealability andtransparency, showed decreased powder leakage, and was suited to afilter for tea.

EXAMPLE 17

A fiber web was obtained by the air lay system from a composite yarn(average yarn diameter of 18 μm, a yarn length of 51 mm) having asheath-core structure that is formed out of a poly(ethyleneterephthalate) (melting point of 265° C.) as a core and a copolymerizedpolyester (melting point of 145° C.) as a sheath. The fiber web in anamount of 10 g/m² and the spun-bonded nonwoven fabric of a polyesterfilaments yarn obtained in Example 6 were stacked. The stacked materialswere passed through smoothing rolls at 160° C. to give a laminate ofnonwoven fabrics. The laminate of nonwoven fabrics thus obtained wasthen coated with a hydrophilic agent in the same manner as in Example 6to give a nonwoven fabric. The nonwoven fabric thus obtained had thefollowing properties: a fabric weight of 22 g/m²; a variation ratio inthe fabric weight of 4.3%; a partial heat contact bonding ratio of 25%;a coating amount of a hydrophilic agent of 0.1% by weight; an averageapparent density of 0.20 g/cm³; a transparency of 67%; a powder leakageratio of 3.2% by weight; a maximum opening diameter of 1,150 μm; andgood hydrophilicity ({circle around (⊙)}). Moreover, the strength of aseal formed by a heat sealing machine at 160° C. was 6.5 N/5 cm(longitudinal) and 4.8 N/5 cm (lateral). The nonwoven fabric wasexcellent in heat sealability and transparency, showed a decreasedpowder leakage, and was suited to a filter for tea.

EXAMPLE 18 Example of Tea Bags

A heat seal bag-making machine of three-dimensional forming type (forforming a tetrahedral shape) was used. The nonwoven fabric obtained inExamples 16 or 17 was slit to give a tape-like fabric 125 mm wide.Strings and tags were bonded to the fabric. The fabric was then foldedin the direction of width (125 mm), and the edges were heat sealed witha width of 5 mm to form a cylindrical shape. The cylindrically shapedfabric was heat sealed at portions corresponding to the bottom portionsat a pitch of 50 mm to give bags.

Two grams of black tea leaves were placed in each bag, and the openingportion of the bag was heat sealed to give a tea bag.

When the tea bag was observed, it was excellent in transparency, and theshape of the tea could be confirmed. When the tea bag was placed in 200ml of hot water in a cup, the bag was submerged under water in 1 second.One could see the black tea leaves in the tea bag spread and swell. Theextracted solution of the black tea was a delicious tea with a powerfulscent.

INDUSTRIAL APPLICABILITY

The nonwoven fabric of the present invention is excellent intransparency, shows decreased powder leakage, has heat sealability, wasexcellent in bag-making processability, and exhibits goodbiodegradability. The nonwoven fabric is therefore useful as a filterfor materials to be extracted such as black tea, green tea and oolongtea.

The tea bag of the present invention prepared by wrapping aparticle-shaped material to be extracted, that is, crushed leaves ofblack tea, green tea, oolong tea, or the like, shows decreased powderleakage, is submerged under hot water without floating when placedtherein, and exhibits quick extraction of the tea components. Inaddition to the above advantages, because the material to be extractedcan be seen from the outside of the tea bag material, the tea bag isparticularly suited when tea leaves such as leaves of high grade blacktea are to be seen through the tea bag material.

1. A nonwoven fabric comprising a thermoplastic synthetic fiber nonwovenfabric having a fabric weight of 7 to 50 g/m², an average fiber diameterof 7 to 40 μm, a partial heat contact bonding ratio of 5 to 30% and acontent of a delustering agent of 0.5% by weight or less, wherein thenonwoven fabric is a laminate of a thermoplastic synthetic fiberspun-bonded nonwoven fabric having an average fiber diameter of 7 to 15μm and a thermoplastic synthetic fiber spun-bonded nonwoven fabrichaving an average fiber diameter of 15 to 40 μm, wherein the nonwovenfabric has a variation ratio of a fabric weight, 10 cm×10 cm, of 10% orless and wherein the nonwoven fabric has a maximum opening diameter of200 to 2,000 μm, and shows a transparency of 50% or more, a powderleakage ratio of 10% by weight or less and a hydrophilicity of less than10 sec.
 2. The nonwoven fabric according to claim 1, wherein thenonwoven fabric is a thermoplastic synthetic fiber nonwoven fabrichaving a fabric weight of 12 to 30 g/m², an average fiber diameter of 12to 30 μm, a partial heat contact bonding ratio of 5 to 30% and a contentof a delustering agent of 0.2% by weight or less, wherein the nonwovenfabric is a laminate of a thermoplastic synthetic fiber spun-bondednonwoven fabric having an average fiber diameter of 12 to 15 μm and athermoplastic synthetic fiber spun-bonded nonwoven fabric having anaverage fiber diameter of 15 to 30 μm, and wherein the nonwoven fabrichas a maximum opening diameter of 400 to 1,650 μm, and shows atransparency of 60% or more, a powder leakage ratio of 5% by weight orless and a hydrophilicity of less than 10 sec.
 3. The nonwoven fabricaccording to claim 1 or 2 wherein the thermoplastic synthetic fiberspun-bonded nonwoven fabric is a spun-bonded nonwoven fabric composed ofa polyolefin filament fiber.
 4. The nonwoven fabric according to claim 1or 2 wherein the thermoplastic synthetic fiber spun-bonded nonwovenfabric is a spun-bonded nonwoven fabric composed of a polyester filamentfiber.
 5. The nonwoven fabric according to claim 4, wherein thethermoplastic synthetic fiber spun-bonded nonwoven fabric is aspun-bonded nonwoven fabric composed of an aliphatic polyester filamentfiber.
 6. The nonwoven fabric according to claim 5, wherein thealiphatic polyester filament fiber is a filament fiber of a polyesterselected from a poly(D-lactic acid), a poly(L-lactic acid), a copolymerof D-lactic acid and L-lactic acid, a copolymer of D-lactic acid and ahydroxycarboxylic acid, a copolymer of L-lactic acid and ahydroxycarboxylic acid, a copolymer of D-lactic acid, L-lactic acid anda hydroxycarboxylic acid, or a blend of these polymers.
 7. The nonwovenfabric according to claim 1 or 2, wherein a synthetic resin or a fibrousmaterial of 2 to 15 g/m² having a melting point lower than that of thethermoplastic synthetic fiber by 30 to 200° C. is laminated to thethermoplastic synthetic fiber nonwoven fabric.
 8. A tea bag prepared byfilling a tea material, to be extracted, into a bag composed of thenonwoven fabric according to claim 1 or 2, and sealing the tea material.9. The tea bag according to claim 8, wherein the bag istetrahedral-shaped.
 10. The tea bag according to claim 8, wherein thetea material to be extracted is black tea, green tea or oolong tea.